One common type of inkjet printer uses a replaceable print cartridge. The replaceable print cartridge contains a printhead and a supply of ink. Often, the print cartridge is not intended to be refillable with ink. Accordingly, when the initial supply of ink is depleted, the print cartridge is replaced; the cartridge is disposed of and a new print cartridge is installed within the scanning carriage.
Frequent replacement of the print cartridge results in a relatively high operating cost. In the cartridge, the printhead is the most relatively expensive component. However, sometimes the printhead has a useable life, which can be significantly longer than the time it takes to deplete the ink within the print cartridge. Accordingly, the printhead is capable of being reused with a refill of ink in the ink supply component of the print cartridge. Because less waste is created, reusing the printhead is environmentally desirable, as well as economical.
Often the print cartridges are refilled intermittently by creating an opening through the print cartridge and automatically refilling the print cartridge with ink. Typically an ink reservoir inside the printer is connected to the print cartridge via a tube or other fluidic connections to refill the ink. Such internal ink supplies, that move with the cartridge, are referred to as on-axis ink supplies. However, the on-axis ink supplies take up significant space, which increases the size of the overall printer. Generally, it is desirable to have the printer take up a minimal amount of space.
Alternatively, the print cartridges are refilled intermittently by creating an opening through the print cartridge and refilling the print cartridge with ink. An external, stationary ink reservoir, such as a flaccid bag containing ink, connected to the scanning print cartridge via a tube is typically provided to refill the ink. Such external ink supplies that don't move with the print cartridge are referred to as off-axis ink supplies. Due to the size of the off-axis ink supplies, including routing of the fluid connections, such as tubes, the minimal size of the printer is significantly increased.
Extended use of the same print cartridge using either refill method creates certain problems. Air bubbles grow in an ink manifold through diffusion and can, upon reaching a certain volume, block flow to the printhead causing print quality defects. Air bubbles may even pressurize the print cartridge during an excursion in the temperature or pressure of the ambient environment from normal operating conditions. In particular, during operation, cool ink flows into the ink manifold and is warmed as it flows toward the printhead. Further, the printhead generates heat as its heater resistors are fired to eject droplets of ink from nozzles. For primarily water-based inks, the solubility of air in ink decreases as the ink is heated. As a result, air is driven out of the solution and coalesces with any preexisting bubbles in the manifold. Moreover, because the warmed ink is expelled from the nozzles and replaced with cool ink, there is a steady supply of air from the warming of the ink that coalesces with the preexisting bubbles in the manifold. Additionally, air from the ambient atmosphere can diffuse into preexisting bubbles in the manifold due to a difference in the partial pressure of water vapor in the bubbles and the ambient environment. Eventually, the entire manifold will fill with air.
Another problem caused by extended use of the same print cartridge include a build-up of paper dust and other fibers on the printhead, which may cause print quality defects when combined with ink mist and dragged across the media during printing.
Often print cartridges have an internal pressure regulator for regulating the flow of ink from an external source into an ink chamber within the print cartridge. Print cartridges with the internal pressure regulator incorporate a diaphragm in the form of a bag. The inside of the bag is open to the atmosphere. The expansion and contraction of the bag controls the flow of ink into the print cartridge to maintain a relatively constant back pressure at the printhead. However, when roughly 5 cc's of air have accumulated in the body and manifold of the print cartridge, the regulator no longer has the capacity to maintain negative pressure. At that point, air in the printhead renders any pressure regulator internal to, or leading to, the print cartridge in a non-functional state. As a result, the back pressure is lost, or the print cartridge is even pressurized (during a temperature or pressure excursion in the ambient environment), and ink drools out of the printhead. A drooling printhead is capable of causing permanent damage to the printer. Moreover, a drooling printhead provides unacceptable print quality. Therefore, the accumulation of excessive air in the body and manifold of print cartridges shortens the useful life of permanent and semi-permanent printheads.
An economical, efficient and compact method for refilling a print cartridge, while maintaining high print quality, is desired.